Coast Survey has issued provisional charts for barge operators and
others traversing Alaska's challenging Yukon River, relying solely on
satellite images to create the electronic navigational charts
that only display shoreline and shoals (shallow areas).
The ENCs,
which display no depth soundings, will give the mariners annually
updated information to help their navigation along the changeable
river.

During a virtual meeting on January 6 with barge operators who
requested NOAA's charting assistance, Andrew Kampia, the cartographer
in charge of the project explained, “You may hear me refer to them as
an experiment because we have not created or released a navigational
product like this before.”
“The Yukon was literally uncharted,” Kampia told the group. “After
some analysis and brainstorming, we decided to create a prototype ENC
using only satellite data. This is unprecedented.”

Coast Survey is not able to provide contemporary surveys to acquire
data for charting the length of the river, as funding, survey vessel
availability, remoteness, and small windows of opportunity to survey
are major obstacles.
Satellite-derived bathymetry from two navigation
seasons between July 2014 and October 2015 helps to fill the void of
contemporary data for Western Alaska.
The charts will help to address the concerns of the local barge
industry that supplies goods and services to western Alaska and who
have had to deal with a lack of data inshore of the 12-foot contour.
(The average draft of vessels transiting up river for village
deliveries is four to six feet.)
The new Yukon River provisional ENCs
US4AK98M, US4AK99M, and US4AK00M offer 1:90,000 scale coverage that
spans the entrance to the Yukon River, including Apoon Pass to Kotlik,
and continues east to Russian Mission.

Satellite-derived bathymetry uses satellite images and histograms
and performs some logarithmic calculations that can sometimes estimate
depths in relatively shallow areas.
Or, as in the case of the Yukon,
satellite-derived bathymetry can estimate shoals, which are displayed
on the Yukon ENCs as obstruction areas.
Unlike traditional hydrography,
however, satellite-derived bathymetry doesn’t provide exact depth
measurements or tidal data at the time the satellite imagery was taken.
“Shoreline depictions are derived from automated processing of
satellite imagery,” Kampia said.
“We felt pretty confident in the
position of the shoreline, but it is below our customary standards, so
we added notes to the ENCs.”

These screenshots show the western entrance to the Yukon River on ENC US4AK98M with zoom

WARNING PROVISIONAL ENC
This ENC was constructed using the best data available. All or much
of the shoreline, depths and shoals within this ENC are below customary
quality, are not corrected for tides, nor based on a known sounding
datum. All or much of the charted detail is highly changeable.
Navigators should use this ENC with extreme caution.
SATELLITE DERIVED DEPTHS
Shoreline, depths, and obstruction areas within the area of this ENC
are derived from satellite imagery from 2015. Their vertical accuracy
is typically ± 2m. Uncharted dangers may exist.

Since the river is in a constant state of change, Coast Survey will
use satellite images after the spring thaws to make annual updates.
Late this spring, a satellite-derived bathymetry analyst will examine
the first satellite images after the Yukon thaws and is navigable.
The Landsat
8 images are available every 16 days as the satellite makes it trip
around the globe, so the first usable images may not be available until
May or June.
After turning the images into shoreline and bathymetric
updates, updated ENCs will be issued in early July – or earlier if
possible.
“We would like to routinize and improve this process over the coming
years based on our analyses,” Kampia said.
“We hope to build on these
successes and use these solutions in areas other than the Yukon, where
traditional surveys aren’t able to provide the charts that navigators
need.”
The Office of Coast Survey recently issued the revised U.S. Arctic Nautical Charting Plan,
but agency officials stress that it is a “living document,” needing
adjustments as priorities change.
Hydrographic and cartographic experts
will travel to Alaska in March to ask the state’s maritime industry
for input that will help future surveying and charting activities for
the State.